Control system for electric motors



Aug. 22, 1950 w. PAYNE 2,519,599

CONTROL SYSTEM FOR ELECTRIC MOTORS Filed Jan. 18, 1946 mPowszSwvy INVENTOR. 4 I 1 7 2:51am //ar /726 iatented Aug. 22, l

UNITED STATES PATENT OFFICE 2,519,599 CONTROL SYSTEM FOR ELECTRIC MOTORS William Harvey Payne, Hinsdale, 111. Application January 18, 1946, Serial No. 641,910 I 14 Claims. (Cl. 314-69) The present invention relates in general to the operation and control of motors, and has more particular reference to control means for motors used in adjusting the electrodes of an electric arc furnace.

The invention, in particular, relates to the control of electromotive means employed for the actuation of hydraulically operated adjusting mechanism for the electrodes of an electric arc melting furnace wherein the electrode element is supported on a movable mounting which, in turn, is supported on an actuating piston operating in an hydraulic cylinder. In such an arrangement the piston is moved in the cylinder, to thus raise and lower and consequently adjust the position of the electrode mounting and the electrode carried thereby, ipiston movement in the cylinder being controlled by delivering and withdrawing regulated quantities of a suitable hydraulic medium to and from the cylinder.

In order to accomplish accurate control and adjustment of the electrode, the liquid hydraulic medium is delivered into and out of the cylinder as by suitable pumping means driven by a suitable motor in response to variations in the electric power delivered to the furnace, such power being a function of variations in the melting are means, however, while performing the useful function of preventing instantaneous reversals of the motive means under full load conditions, tend to defeat the anti-hunting purpose by delaying the reversing action of the motive means so that hunting is not eliminated but is merely caused to take place more slcwly.

Systems heretofore provided for positioning the relatively heavy electrode mounting and associated parts have required large, powerful and heavy motors for pump driving punposes; and the consequently large over-all inertia of the parts to be moved increases the difiiculty of bringing the mechanism accurately and rapidly to a desired adjusted position. Furthermore, the necessity of employing large and powerful adjusting motors, together with elaborate anti-hunting and other control equipment, very appreciably increases the cost of installation.

Although the invention will hereinafter be described particularly in its aspects relating to the positioning of arc furnace electrodes, it will be apparent that the system may be applied to formed at the electrode, in the furnace, when a the same is in operation.

Among the several operational difficulties encountered in control apparatus of the character mentioned is the tendenc of the motive mechanism to hunt. Hunting is due, in part, to the considerable weight and inertia of the electrode supporting elements and the necessity of moving such heavy structure into precisely adjusted position. As a consequence, the motive means may move the structure to be adjusted beyond the required adjusted position, whereupon the reversal of the motive means may return the adjusted parts again through and beyond the required adjusted position, such repeated reversing of the motive means, in its effort to reach an exact position of required adjustment, being termed hunting; and various expedients have been proposed in an effort to minimize hunting in motive means of the character described.

Among such expedients heretofore proposed, has been the provision of dampening devices, such as oil-pots for retarding theoperation of the motive means, in an effort to cause the same to approach a desired adjusted position relatively slowly and thus to minimize hunting due to over-travel of the parts being adjusted beyond the required adjusted position. Such dampening other industrial services and consequently is not necessarily limited to the control of arc furnace electrodes.

An important object of the present invention is to provide a new and improved control for driving motors and particularly motors used in operating hydraulic positioning apparatus; a further object being to provide simple and ineX- pensive control mechanism that is installable at relatively low cost, and [which will give substantially trouble-free service throughout extended service life.

Another important object is to utilize relatively small driving motors for electrode adjusting purposes, in conjunction with the improved control mechanism of the present invention; a further object being to provide control mechanism and associated arc furnace electrode adjusting means making possible the utilization of small adjusting motors, such as fractional horsepower motors for accomplishing the adjustment of relatively heavy electrode supporting parts, for the adjustment of which it has heretofore been considered essential to employ relatively large motors having horsepower ratings of the order of three horsepower and more.

Another important object is to provide a control for motors of relatively low power thereby materially reducing not only the cost of motor equipment for the adjustment of arc furnace electrodes, but also appreciably reducing the cost of motor control equipment required for controlling such electrode adjusting motive means.

Another important object is to provide a. motor driven adjusting system having low electrical lag and corresponding rapidity of response; a further object being to provide an adjusting system adapted to operate substantially without hunting.

The foregoing and numerous other important objects, advantages and inherent functions of the invention will become apparent as the same is more fully understood from the description, which, taken in connection with the accompanying drawings. discloses preferred embodiments of the invention.

Referring to the drawings:

Fig. 1 is a schematic view of electrode adjusting equipment embodying the present invention. the view showing one phase only of a normally multiphase electric arc melting furnace; and

Fig.2 is a -wiring diagram showing a modified arrangement of control equipment.

To illustrate the invention, the drawings show adjusting mechanism particularly adapted for the support'and adjustment of the electrodes of an electric arc furnace. Such a furnace may comprise a shell provided with a roof having an opening for the reception of the electrodes in said openings. Ordinarily there are several electrodes each having its separate adjusting apparatus, but since the'adjusting apparatus is the same for each electrode, it will be sufiicient to describe one electrode and its associated equipment.

The shell of the furnace, on one side, may carry a bracket fitted with preferably roller means forming a guide for a hollow vertical extension |2 having a horizontal electrode supporting arm it at its upper end. The arm |3 may overlie the opening in the roof of the furnaceand carry the electrode in position extending into the furnace through said opening. The arm l3 also is preferably insulated from the vertical extension l2, and may carry suitable electrical power supply conduits for connecting the electrode with a suitable power source, such as a transformer. The vertical extension i2 and the arm |3 thus constitute a vertically movable mounting for the electrode. By moving the mounting upwardly and downwardly with respect to the furnace, in the support rollers l I, the electrode may be raised and lowered in arcing position in the furnace.

The furnace and electrode may be. of any standard or conventional design. the furnace being lined with refractory material, as is well understood in the art. The furnace is adapted to contain a charge of metal to be melted and may embody a pouring spout and means for tilting the furnace whereby its molten contents may be poured out through the spout. Electrical power may be supplied to the furnace electrode from a suitable power source, one side of which may be connected to ground, and the other connected to the electrode, as by means of a bus bar l4 anda flexible conductor l5 connected with the electrode, as through the support arm i3, the frame of the furnace being grounded or otherwise suitably connected with the grounded side of the power source.

With a normal charge of metal to be melted in the furnace, power may be supplied to the electrode from the power source. When the electrode is adjusted in contact with the metal charge in the furnace, electric current will flow through the scrap from the electrodes causing arcs to be formed between the electrodes and the metal charge in the furnace. Heat from the arcs serves to melt the charge in a manner well known in the art.

A piston I8 and a cooperating cylinder I! may be provided within the hollow, vertical extension [2 for the purpose of moving the electrode mounting in order to adjust the position of the electrode in the furnace. To this end, the electrode mounting l3 may be supported on the upper end of the piston I6. The lower end of the cylinder |'I may be mechanically supported. as on a suitable bracket, at the bottom of the furnace shell so that the piston and cylinder may move with the furnace when the same is tilted for the pouring of molten metal therefrom. The lower end of the cylinder I1 projects below the working end of the piston and is connected to a conduit or pipe it through which a suitable liquid hydraulic fluid may enter or be withdrawn from th cylinder in order to move the piston therein an thus raise or lower the electrode in the furnace.

The cylinder connected end of the conduit l8 may embody a flexible portion to accommodate the tilting of the cylinder .with the furnace during the metal pouring operation. The conduit It may be connected to a pump l9 and associated conduit network 20 embodying flow control valves 2|, 2|, 22 and 22', the network being connected as by a suction conduit 23 and a return conduit 24 with a. reservoir 25 containing a supply 26 of liquid hydraulic medium.

By driving the pump in one direction, the hydraulic medium may be drawn through the suction pipe 23, thence through the check valve 2| and delivered thence through the pipe l3 and the conduit l8 into the cylinder I! in order to raise the electrode support. By reversing the pump, the hydraulic medium may be withdrawn from the cylinder il through the conduit l8 and the pump l9 and delivered thence through the valve 22 and the return pipe 24 to the reservoir 25. A baflle 21 is preferably disposed within the reservoir between the ends of the suction and discharge pipes 23 and 24. The valves 2| and 2| are preferably check valves allowing fluid flow therethrough from the pipe 23 toward the pump. The valves 22 and 22', however, are preferably spring-load valves permitting fluid flow in one direction from the pump to the discharge pipe 24, only when pump pressure exceeds the adjusted spring pressure on said valves. As a consequence, the pump will normally function to deliver and withdraw liquid to and from the cylinder |l through the valves 2| and 22. If, however, the piston is reaches either the upper or lower limit of its operating range. continued operation of the pump in one direction, when the piston is at the lower limit of its travel in the cylinder, will cause the pump merely to circulate liquid through the pipe 23, the valve 2|, the pump IS, the valve 22, and the conduit 24. Continued operation of the pump I9, in the reverse direction, when the piston is at the upper limits of its adjusting movement will cause recirculation of liquid through the pipe 23, the valve 2|, the pump I9, the valve 22', and the return pipe 2 The tank 25 may contain gas, under pressure. in addition to the liquid medium 26, in order to counterbalance the weight of the electrode and its associated parts. Air, or other gas for counterbalancing purposes, may be supplied to the tank through a fitting 28 which may comprise valve means for obtaining a desired gaseous pressure in the tank. The tank may be filled with air, under pressure, as from a shop air pressure system, or air may be supplied to the tank directly from a compressor and associated compressed air storage tank. The apparatus may thus comprise an air or gas pressure counterbalanced system for supporting the electrode floatingly at the furnace, in combination with a motor driven pump l9 for moving the hydraulic medium to alter the elevation at which the electrode is supported.

The pump l9 may be drivingly connected with an electric motor 29, and control means 30 is provided for driving the motor in response to electrical arcing conditions prevailing at the electrode when the same is in operation.

The motor 29 preferably comprises a direct current motor having a field winding 3| energized from a suitable power source 32 at all times when the system is in operation. Power is supplied to the armature of the motor 29 from the bus II by way of the control means 30, which comprises a transformer 33, the secondary of which is coupled with the bus bar H. The transformer is connected in circuit with a current flow indicating ammeter 34, a current flow adjusting rheostat 35, and a rectifier network 36, one side of the input of said rectifying network being connected to ground. The control means 30 also includes a rectifying network 31, the input to which is connected, on one side, to ground, and on the other side to the bus H by means of a voltage lead 38. Suitable reactive means, if necessary, may be used in either the voltage or the current supply circuit to bring both in phase, by offsetting an phase displacement produced by the current transformer 33.

As shown in Fig. 1, the rectifying networks 36 and 31 are interconnected in series, the positive delivery side of each network being connected to the negative delivery side of the other; and the armature of the motor being connected in shunt relation with respect to each rectifier. As a consequence, when the direct current outputs of the networks 36 and 31 are equal, there will be zero electrical potential applied to the armature of the motor. When the direct current output of either of the rectifying networks exceeds the direct current output of the other, actuating potential will be applied to the armature of the motor to drive the same in one direction or the other depending upon which of the networks is delivering the greater current. The motor 29 thus will be driven at a speed and in a direction determined by the difference in the direct current outputs of the networks 36 and 31 and the polarity thereof.

Those skilled in the art can see that either the rectifier network 30, or associated balancing resistors 36 and 31 constitute dynamic breaking circuits for motor 29. If desired, however, additional dynamic braking means, such as a resistance 39, may be connected in parallel relationship across the armature of the motor 29, such braking resistance 39 being under the control of a relay switch 40, the operating solenoid M of which is connected in series vwith the armature of the motor. Upon the application of driving power to the armature of the motor in either direction, the switch 40 will be opened by the action of the solenoid 4|. As soon, however, as zero potential is applied to the armature of the motor, as when the direct current outputs of the networks 36 and 31 are equal, the switch 40 will close in order thus to apply the dynamic braking eifect of the resistance 39 to the motor armature.

From the foregoing it will be seen that power delivered through the current transformer 33 will be made eflective in one direction upon the motor 29 through the rectifying means 39, such power being onset against opposing power delivered to the motor through the rectifying means 31. So long as the power delivered through the rectifier 33 is equal to the power delivered through the rectifier 31, the motor will remain stationary. Power delivered through either rectifier, in excess of that delivered through the other, will cause the motor to turn in a corresponding direction, motor movement diminishing as the power delivered by the rectifiers becomes equal, at which time the dynamic braking means 39 and 40 operate to stop motor movement instantly.

It will be seen also that motor driving power delivered through the rectifier 33 will be a function of current flow in the bus l4 while the power delivered by the rectifier 31 will be a function of bus voltage; The current and voltage of the bus 14, in turn, vary in accordance with arcing conditions at the electrode being controlled, and consequently, the arrangement illustrated and described will cause the motor 29 to operate in reponse to electrode arcing conditions. Whenever electrode arc characteristics reflect a condition in which the electrode is displaced, in either direction, from a desired operating position, the motor 29 will be driven in a direction to return the electrode to the desired operating position, under the control of current and voltage conditions, in the bus and therefore proportionally to are values. Consequently, the motor will respond instantly to any abnormal arc values in order to return the same to desired normal values by moving the electrode to the desired operating position.

As shown in Fig. 2, the rectifying networks 36 and 31 are interconnected in para lel, corresponding output sides of the networks being connected directly together and the remaining output sides of both networks being connected, respectively, through adjustable resistors 36' and 31' to said directly connected output sides, the armature of the motor 29 being also connected between said remaining output sides of the networks. A switch 40' having a shunt connected operating coil 4 I may be connected in series with the armature of the motor 29 for dynamic braking purposes, the switch functioning, like the corresponding switch 40 in Fig. l, to connect a braking resistor 39 with the motor armature, as the coil 4| becomes de-energized.

When the output of one rectifier, as adjusted by its corresponding resistor, is equal to the output of the other, as adjusted by its resistor, the potential difference between the motor connected output sides of the networks will be zero and the motor will consequently be stationary. If the direct current output of either network exceeds that of the other, the potential difference between the motor connected sides of the networks will provide motor energizing current to the armature of the motor to cause it to turn in a direction determined by which of said rectifiers is, at the moment, delivering a greater amount of power than the other. As a consequence, the motor 29, in Fig. 2, will be driven in one direction or the other in response to any off-balance condition in the are produced at the electrode being controlled.

The arrangements described above, thus employ electrical conditions in the bus II. which correspond with prevailing conditions in the arc, to maintain the electrode at all timesin a position to maintain an arc having desired arc values, the system operating whenever the arc is oil balance, to operate the motor and connected pump I! in a direction and at a speed proportiont al to the electrode displacement from the desired operating position to return the electrode accurately and rapidly to such position.

It will be noted that the system inherently provides minimum over-all electrode moving inertia for the reason that the weight of the electrode and its mounting is counterbalanced by means of pressure in the tank 25. As a consequence, the pump and its driving member need be only powerful enough to accomplish electrode movement. The motor thus may be of relatively small size and may have a rating of the'order of a fractional horsepower, the small size of the motor in turn minimizing the inertia of operating mechanism, with the result that the system will respond rapidly both in starting the motor to adiust the electrode, and in stopping the motor when the electrode is in adJusted position, thereby substantially eliminating motor hunting. The control apparatus described herein fulfills its intended purpose efliciently and efiectively and is cilfiaracterized by simplicity, low cost and long 1 6.

It should be understood that the invention is not necessarily limited to the details herein set forth since the same may be modified and numerous changes may be made within the scope of the appended claims, without departing from the spirit or scope of the invention.

The invention is hereby claimed asfollows:

1. Mechanism for controlling a direct current electric motor in accordance with voltage and current conditions in a power supply line, comprising a pair of rectifiers energized from said line respectively in proportion to voltage, and current conditions prevailing in said line, said rectiflers having output sides differentially directly connected with the motor to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers, and means operable to adjust the energy output of each of said rectifiers.

2. Mechanism for controlling a direct current electric motor in accordance with voltage and current conditions in an alternating current power supply line, comprising a pair of rectifiers, circuit means to energize said rectiflers from said supply line respectively in proportion to voltage and current conditions prevailing in said line, and means directly to connect the output sides differentially with the motor to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers. V

3. Mechanism for controlling a direct current electric motor in accordance with voltage and current conditions in an alternating current power supply line, comprising a pair of rectifiers, circuit means to energize said rectiflers from said supply line respectively in proportion to '4. Mechanism for controlling a direct current electric motor in accordance with voltage and current conditions in an alternating current power supply line, comprising a pair of rectifiers, circuit means to energize said rectifiers respectively in proportion to voltage and current conditions prevailing in said line, circuit means directly interconnecting the power output sides voltage and current conditions prevailing in said line, means directly to connect the output sides differentially with the motor to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers, one of said rectifiers being energized from said supply line through a transformer. and means operable to adjust the power supplied to the rectifier through said transformer.

of said rectifiers with the armature of said motor, whereby to energize the same for operation in one direction or the other in accordance with the difierential output of said rectifiers, y amic brake means comprising a braking resistor and a normally opening relay switch connected in series therewith to form a circuit connected between the opposite sides of the armature of said motor, and a switch opening coil for said relay switch connected in series with said armature.

5. Mechanism as set forth in claim 4, wherein the positive output side of each rectifier is directly connected with the negative-output side of the other rectifier, the circuit comprising the armature and coil, and the circuit comprising the switch and resistor, being connected between said interconnected output sides of the rectifiers.

6. Mechanism as set forth in claim 4, wherein one side of the output of one of the rectifiers is directly connected to the output side of like polarity of the other rectifier, the circuit comprising the armature and coil, and the circuit comprising the switch and resistor, being interconnected between the other output sides of said rectifiers.

7. Mechanism for adjustably positioning an alternating current electric arc furnace electrode, in response to electrical variation in are power conditions, comprising the combination, with an alternatmg current power supply line for supplying are power to the electrode, of a direct current motor drivingly connected to move the electrode, and a pair of rectifiers energized from said line and having output sides differentially directly connected with the motor to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers.

8. Mechanism for adjustably positioning an alternating current electric arc furnace electrode, in response to electrical variation in are power conditions, comprising the combination, with an alternating current power supply line for supplying are power to the electrode, of a direct current motor drivingly' connected to move the electrode, a pair of r'ectifiers energized from said line and having output sides difierentially directly connected with the motor to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers, and means operable to adjust the energy output of each of said rectifiers.

9. Mechanism for adjustably positioning an alternating current electric arc furnace electrode, in response to electrical variation in are power conditions, comprising the combination, with an alternating current power supply line for supplying arc power to the electrode, of a direct current motor drivingly connected to move the electrode, a pair of rectifiers, circuit means to energize said rectifiers from said supply line respectively in proportion to voltage and current conditions prevailing in said line, and means directly to connect the output sides of said rectifiers difierentially with the motor to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers.

10. Mechanism for adjustably positioning an alternating current electric arc furnace electrode, in response to electrical variation in are power conditions, comprising the combination, with an alternating current power supply line for supplying are power to the electrode, of a direct current motor drivingly connected to move the electrode, a pair of rectifiers, circuit means to energize said rectifiers from said supply line respectively in proportion to voltage and current conditions prevailing in said line, means directly to conrect the output sides of said rectifiers differentially with the motor to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers, one of said rectifiers being energized from said supply line through a transformer, and means operable to adjust the power supplied to the rectifier through said transformer.

11. Mechanism for adjustably positioning an alternating current are furnace electrode, in response to electrical variations in are power conditions, comprising the combination, with a supply line for supplying alternating current are power to the electrode, of a direct current motor drivingly connected to move the electrode, a pair of rectifiers, circuit means to energize said rectifiers from said supply line respectively in proportion to voltage and current conditions prevailing in said line, circuit means directly interconnecting the power output sides of said rectifiers with the armature of said motor, whereby to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers, dynamic brake means comprising a braking resistor and a normally opening relay switch connected in series therewith to form a circuit connected between the opposite sides of the armature of said motor, and a switch opening coil for said relay switch connected in series with said armature.

12. Mechanism for adjustably positioning an alternating current are furnace electrode, in response to electrical Variations in are power conditions, comprising the combination, with a supply line for supplying alternating current are power to the electrode, of hydraulic means including a pump for adjustably moving the electrode, a direct current motor drivingly connected with said pump, a pair of rectifiers, circuit means to energize said rectifiers from said supply line respectively in proportion to voltage and current conditions prevailing in said line, circuit means directly interconnecting the power output sides of said rectifiers with the armature of said motor, whereby to energize the same for operation in one direction or the other in accordance with the differential output of said rectifiers, dynamic brake means comprising a braking resistor and a normally opening relay switch connected in series therewith to form a circuit connected between the opposite sides of the armature of said motor, and a switch opening coil for said relay switch connected in series with said armature.

13. Mechanism as set forth in claim 11, wherein the positive output side of each rectifier is directly connected with the negative output side of the other rectifier, the circuit comprising the armature and coil, and the circuit comprising the switch and resistor, being connected between said interconnected output sides of the rectifiers.

14. Mechanism as set forth in claim 11, wherein one side of the output of one of the rectifiers is directly connected to the output side of like polarity of the other rectifier, the circuit comprising the armature and coil, and the circuit comprising the switch and resistor, being interconnected between the other output sides of said rectifiers.

WILLIAM HARVEY PAYNE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,241,574 Sykes Oct. 2, 1917 1,449,879 Boddie Mar. 27, 1923 1,535,883 Winne Apr. 28, 1925 2,132,479 Holslag Oct. 11, 1938 2,137,877 Kramer Nov. 22, 1938 2,259,958 Levy Oct. 21, 1941 2,265,687 Chapman Dec. 9, 1941 2,327,357 Lilia Aug. 24, 1943 2,329,127 Levy Sept. 7, 1943 2,389,164 Payne Nov. 20, 1945 2,399,363 Levy Apr. 30, 1946 2,399,387 Reilly Apr. 30, 1946 2,412,000 Moore Dec. 3, 1946 

